(1) Field of the Invention
The present invention relates to a fluorescent lamp, and particularly relates to a fluorescent lamp that has a phosphor layer formed on an inner surface of its lamp vessel.
(2) Related Art
One kind of fluorescent lamps having a lamp vessel whose inner surface is formed a phosphor layer is electrodeless fluorescent lamp. The electrodeless fluorescent lamp is a fluorescent lamp that literally does not have any electrode. The electrodeless fluorescent lamp is getting attention since it has longer life than other kinds of fluorescent lamps whose life is mainly determined by electrode.
One type of such electrodeless fluorescent lamps has a structure of having a lamp vessel that has a tube-like concave portion whose hollow is formed like a tube, and a coil is provided in the concave portion. If alternating current having a high frequency is fed to the coil, an alternating magnetic field is generated inside the lamp vessel. This alternating magnetic field makes mercury atoms and electrons collide with each other in the lamp vessel, thereby making the mercury atoms emit ultraviolet light. The ultraviolet light emitted in this way will be irradiated on the phosphors applied on an inner surface of the lamp vessel, so as to generate visible light.
In relation to a method of producing the lamp vessel of the aforementioned electrodeless fluorescent lamp, the following mainly describes a process of applying phosphors, a process of drying thereof, and a process of removing unnecessary phosphors.
FIG. 1 is a diagram showing a series of steps adopted by the conventional technology.
An object shown in (a)–(d) of FIG. 1 which is formed as a flask having a round-bottom is a glass vessel 106, a part of which is used for a glass bulb 102 (see FIG. 2) of a lamp vessel 100 (see FIG. 2) Note that each glass vessel 106 in (a)–(d) of FIG. 1 is in a longitudinal sectional view.
First, an application solution 110 containing phosphor powders is injected into the glass vessel 106 whose opening is directed upward, with use of an injection nozzle 108, up to a level shown in FIG. 1(a) (so far, refer to FIG. 1(a)).
Next, the glass vessel 106 is made to stand in an inverted position, being rotated in the direction of the arrow D, so as to let out an excess of the application solution 110 from the glass vessel 106 (FIG. 1(b)). Here, the reason why the glass vessel 106 is rotated is to make the thickness of the application solution 110 attached to the inner surface of the glass vessel 106 as even as possible.
Then, while the glass vessel 106 is in an inverted position, a warm-air nozzle 112 is entered into the glass vessel 106, so as to dry the application solution 110 attached to the inner surface of the glass vessel 106 (FIG. 1(c)). Here, the reason why the drying step is performed while the glass vessel 106 is in an inverted position is to prevent the application solution. 110 from being accumulated at the bottom of the glass vessel 106, which results in making the thickness of the formed phosphor layer uneven.
After the application solution 110 is dried, and so the phosphor layer 114 is formed, unnecessary phosphor is removed which has been formed on the inner surface of the cylindrical part 116 of the glass vessel 106. For this removing step, a rubber blade 118 is used for example. This rubber blade 118 is inserted just before the spherical part 120 of the glass vessel 106. The reason why the rubber blade 118 is not inserted inside the spherical part 120 beyond the cylindrical part 116 will be detailed later. The rubber blade 118, by being rotated, scrapes the phosphor layer 114 off the inner surface of the cylindrical part 116(FIG. 1(d)). The following is the reason why the phosphor layer 114 is removed from the cylindrical part 116. That is, an internal tube 104 (detailed later) will be attached to the cylindrical part 116 by means of melting. In view of this, if there is phosphor left in the cylindrical part 116 which will be attached to the internal tube 104, a crack will likely occur in the attaching process, and further there is a possibility of leak due to incomplete attachment therebetween.
After the phosphor layer is formed at a predetermined area of the inner surface of the glass vessel 106 as aforementioned, an internal tube 104 is inserted therein as shown in FIG. 2, thereby determining the position of the internal tube 104. This internal tube 104 will be a storage of the coil. Then, a burner is used to heat the part of the external surface of the cylindrical part 116 that corresponds to an opening of the internal tube 104, while the internal tube 104 and the glass vessel 106 are being rotated around the tube axis of the internal tube, in a same direction and at a same speed. This operation attaches together the internal tube 104 and the glass vessel 106 by means of melting (hermetic sealing). Then, the part of the glass vessel which is shown in the broken line is cut, so as to complete the lamp vessel 100.
However, in the aforementioned lamp vessel 100, the edge of the phosphor layer 114 is square-cornered, as shown in “details of part E” of FIG. 2. This is because the phosphor layer 114 is removed by the rubber blade 118. Accordingly, at this angular part 122, some portions thereof are likely to fall off (chipping). When the electrodeless fluorescent lamp is illuminated, the pieces of the phosphor having fallen off will be seen as a shadow, from outside the electrodeless fluorescent lamp, which is a quality problem.
Note here that the reason why the rubber blade 118 is not inserted inside the spherical part 120 beyond the cylindrical part 116 is as follows. That is, if the phosphor layer is scraped off by inserting the rubber blade in such a way, the phosphor that has been scraped off will be stuck, in-powder forms, in the slope part 124 which is arc-shaped, the slope part 124 positioning between the cylindrical part 116 and the spherical part 120. If such remaining phosphor powders enter into the attaching part in the aforementioned attaching process, a crack or a leak occurs at the attaching part.